Hi, I'll worry about the learning curve of beginners. Maybe, beginners will try following session in their 1st week. ghci> :t foldr ghci> :t ($) They'll get following result. Before ghc7.8: Prelude> :t foldr foldr :: (a -> b -> b) -> b -> [a] -> b Prelude> :t ($) ($) :: (a -> b) -> a -> b Beginners should only understand about following: * type variable (polymorphism) After ghc8.0: Prelude> :t foldr foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b Prelude> :t ($) ($) :: forall (w :: GHC.Types.Levity) a (b :: TYPE w). (a -> b) -> a -> b Beginners should understand about following things, more: * higher order polymorphism (t m) * type class (class t =>) * universal quantification (forall) * kind (type::kind) * levity (lifted/unlifted) I think it's harder in their 1st week. I tried to draw informal illustrations about Foldable, but beginners may need ghci-beginner’s mode or something? Sorry I don't still have good idea. Of course I like Haskell's abstraction :) Regards, Takenobu 2016-02-05 18:19 GMT+09:00 Joachim Breitner <mail@joachim-breitner.de>:
Hi,
Am Freitag, den 05.02.2016, 09:22 +0200 schrieb Roman Cheplyaka:
On 02/05/2016 01:31 AM, Edward Z. Yang wrote:
I'm not really sure how you would change the type of 'id' based on a language pragma.
How do people feel about a cosmetic fix, where we introduce a new pragma, {-# LANGUAGE ShowLevity #-} which controls the display of levity arguments/TYPE. It's off by default but gets turned on by some extensions like MagicHash (i.e. we only show levity if you have enabled extensions where the distinction matters).
Yes, I am surprised this isn't the way it's been done. The levity arguments should totally be hidden unless requested explicitly.
I'd only expect this to be a ghc flag (-fshow-levity), not a language pragma, since it should only affect the way types are /shown/.
shouldn’t this already happen, based on -fprint-explicit-kinds? At least I would have expected this.
So we probably either want to make sure that -fno-print-explicit-kinds also prevents forall’ed kind variables, or add a new flag of that (heh) kind.
Greetings, Joachim
-- Joachim “nomeata” Breitner mail@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata@debian.org
_______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs